The severity of coronary stenosis can be analyzed anatomically and functionally. Anatomic severity is measured in geometric terms by quantitative arteriography. Functional severity is determined by directly measured coronary flow, pressure gradient and coronary flow reserve. In theory, anatomic and functional approaches to quantifying stenosis severity should be interchangeable, mathematically and experimentally equivalent since they are derived from common fluid dynamic principles. To document this equivalency, the Specific Aims are to test the following hypothesis: (1) Coronary flow reserve (CFR) of a stenotic coronary artery can be accounted for or predicted by arteriography from all the geometric dimensions of a stenosis-length, relative % narrowing, absolute diameter under measured or controlled conditions of aortic pressure, coronary vasoconstrictor tone or significant collateral flow. (2) Failure to account for one or more dimensions of a stenosis causes significant errors in the x-ray prediction of CFR even where there may be a correlation between CFR and a given single dimension. (3) Collateral circulation sufficient to provide normal resting flow does not cause a significant error in the x-ray prediction of CFR due to low flow capacity of collaterals. (4) Coronary flow reserve is accurately predicted from all stenosis dimensions over a wide range of coronary vasoconstrictor tone. (5) Neither flexible wall collapse of stenoses, changing flow velocity profiles nor entrance effects cause significant errors in x-ray prediction of CFR. This study will demonstrate that coronary flow reserve measured directly or predicted by quantitative coronary arteriography is a single measure of stenosis severity accounting for all its geometric characteristics and will establish the relation between functional and anatomic descriptors of stenosis severity suitable for routine clinical application.